Patent Application
20100178444
The present invention relates to a rubber member for tires that helps to improve uniformity of the tires and prevent defective molding. The present invention also relates to a method for producing the rubber member and a method for producing a pneumatic tire.
Pneumatic tires are comprised of various rubber members such as tread rubber, sidewall rubber, clinch rubber, cushion rubber, and inner liner rubber. Conventionally, these rubber members are molded by being extruded in predetermined cross sections from, for example, rubber extruders. A drawback is that the method necessitates a nozzle for the rubber extruder on a cross sectional basis and a long period of time for the replacement work.
A proposed solution to the drawback is, as shown in
The strip wound assembly (b) can be easily formed with any desired cross section by, for example, varying the pitch of winding the rubber strip. This eliminates the conventional need for preparing various kinds of nozzles and the trouble of replacing them. This method eliminates intermediate stock of the rubber members by, for example, forming the strip wound assembly (b) directly on the peripheries of constituents of the tire, thereby reducing in-process material for rubber members and providing the advantage of further enhancing the production efficiency of tires.
Patent document 1: Japanese unexamined Patent Application Publication No. 2006-51711.
Incidentally, when a rubber member of a pneumatic tire is molded from the rubber strip (S), the winding count of the rubber strip (S) can be made smaller as the thickness thereof increases. That is, the strip wound assembly (b) can be formed in a shorter period of time, thereby improving the productivity of pneumatic tires.
However, as shown in
Further, as shown in
It is an object of the present invention to provide a rubber member for tires that is capable of inhibiting defective molding and degraded uniformity of the tires, and to provide a method for producing the rubber member, and a method for producing a pneumatic tire.
According to a first aspect of the present invention, a rubber member for tires, formed of a spirally wound unvulcanized rubber strip having a first longitudinal end portion for serving as a starting side of winding of the rubber strip and a second longitudinal end portion for serving as an ending side of the winding. Each end surface of the first end portion and the second end portion has a front end edge extending, in plan view, from one side edge to another side edge of the rubber strip in the width direction thereof. The end surface of at least one of the first end portion and the second end portion is an inclined surface inclining to the longitudinal direction line of the rubber strip.
A second aspect of the present invention is drawn to a method for producing the rubber member for tires according to the first aspect of the present invention, and includes the steps of:
attaching the first longitudinal end portion of the rubber strip to an substantially cylindrical object;
spirally winding the rubber strip onto the cylindrical object; and attaching a second longitudinal end portion of the rubber strip to a wound assembly of the rubber strip formed in the winding step. The each end surface of the first end portion and the second end portion has a front end edge extending, in plan view, from one side edge to another side edge of the rubber strip in the width direction thereof. The end surface of at least one of the first end portion and the second end portion is an inclined surface inclining to the longitudinal direction line of the rubber strip.
A third aspect of the present invention is drawn to a method for producing a tire includes the steps of:
forming green tire by using the rubber member for tires according to the second aspect of the present invention; and vulcanizing the green tire.
In the first aspect of the present invention, at least one of the first end portion and the second end portion of the rubber strip has an end surface inclining to the longitudinal direction line of the rubber strip. As the above-mentioned inclined surface, an inclined surface which is inclined to reduce the thickness gradually toward a front end edge may be used. In such an inclined surface which thickness changes, this eliminates occurrence of a large step at the end with the inclined surface, thereby improving uniformity. This also prevents occurrence of a large air pocket when the end is covered with a succeeding wound portion of the rubber strip. As a result, defective molding and degraded durability of pneumatic tires are inhibited.
As the above-mentioned inclined surface, an inclined surface in which the front end edge of the inclined surface is inclined to the longitudinal direction line may be adopted. In case of such an inclined surface of the inclining front end edge, this alleviates variation in mass and rigidity in the circumferential direction and thereby improves uniformity. Since the front end edge is inclined, when the end is covered with a succeeding wound portion of the rubber strip, air between portions of the rubber strip is easily discharged outside the rubber member along the front end edge. That is, this makes air hard to be confined, thereby preventing occurrence of a large air pocket.
a) and 4(b) are cross sectional views of rubber members each made of a strip wound assembly made using the rubber strip.
a) and 5(b) are cross sectional views respectively corresponding to the lines A-A and B-B in
a) and 6(b) are cross sectional views of an inclined surface of the rubber strip.
a) and 10(b) are plan views of the rubber strip in a wound state according to other embodiments of the present invention.
a) and 22(b) are circumferential cross sectional views of the conventional rubber strip showing the ends thereof.
10 front end edge
12 end surface
13 inclined surface
24 cutting apparatus
24
a cutting device
30 sharp cutting edge
30
b root portion
31 pressing portion
31
a pressing face
E1, E2 side edges
e1, e2 end portions
Fx longitudinal direction
G rubber member
S rubber strip
Ss surface
Hereinafter, an embodiment of the present invention will now be described on the basis of drawings.
Each of the carcasses 6 is formed of at least one carcass ply 6A having carcass cords disposed at an angle of, for example, 70 to 90 degrees relative to the circumferential direction of the tire. At an axially outer side of each of main body portions 6a extending from the tread portions 2 through the side wall portions 3 to the bead cores 5 in the bead portions 4, the carcass ply 6A has a turned-up portion 6b extending from the main body portion and turned up from an axially inner side to an axially outer side over the bead core 5. The belt layer 7 is composed of, in this example, two belt plies 7A and 7B having belt cords disposed at an angle of, for example, 10 to 35 degrees relative to the circumferential direction of the tire.
As main rubber members, the pneumatic tire 1 includes a tread rubber (G1) disposed at a radially outer side of the belt layer 7, a side wall rubber (G2) disposed at an axially outer side of the carcass 6 in the side wall portion 3, an inner liner rubber (G3) made of air impermeable rubber and disposed at an axially inner side of the carcass 6, a clinch rubber (G4) disposed at an axially outer side of the carcass in the bead portion 4 and having excellent abrasion resistance, a cushion rubber (G5) disposed at both sides of and at a radially inner side of the belt layer 7 and having an substantially triangle cross section, and a hard bead apex (G6) extending radially outwardly in a tapered manner from the bead core 5.
For at least one of the rubber members (G1) to (G6), the pneumatic tire 1 uses a rubber member (R), which, as schematically shown in
The rubber member (R) is produced by a production method including the steps of:
(1) attaching a first longitudinal end portion (e1) of a rubber strip (S) to the cylindrical object (u);
(2) spirally winding the rubber strip (S) onto the cylindrical object (U); and
(3) attaching a second longitudinal end portion (e2) of the rubber strip (S) to a wound assembly of the rubber strip formed in the winding step.
The cylindrical object (U) is not particularly specified insofar as it is cylindrical. Examples of the cylindrical object (U) include, as well as a molded drum, the carcass 6 and the belt layer 7, which constitute part of the green tire. That is, the rubber strip (S) may be directly wound onto the periphery of the carcass 6 or the belt layer 7, thus forming the rubber member (R). The attachment of the end portions (e1) and (e2) is secured by the viscosity of the unvulcanized rubber.
Next, as shown in
In the inclined surface 13, this eliminates occurrence of a large step at the end portions (e1) and (e2) of the rubber strip (S) of the rubber member (R), as shown in
specifically, as shown in
Thus, forming a green tire from the rubber member (R) and vulcanizing the green tire realizes production of a pneumatic tire with superior uniformity. In the pneumatic tire thus produced, a large air pocket scarcely occurs at the end portions (e1) and (e2) of the rubber strip (S). This prevents pneumatic tires from meeting with defective molding and degraded durability that would otherwise be caused by the air pocket.
a) shows a cross sectional view taken on line C-C of
The inclined surface 13 may have a uniform inclination angle θ as shown in
More preferably, all the inclination angles θ1, θ2, . . . , θn meet the range.
θ=Σ(θ·Li)/ΣLi (i=1, 2, . . . n)
where θi denotes the inclination angle of the end portions (e1) and (e2) of the rubber strip (S), and Li denotes the length over which the angle θi is secured.
Referring to
On the other hand, making the thickness (t) and the width (W) of the rubber strip (S) excessively large tends to degrade the workability of winding the rubber strip (S) onto the cylindrical object (U) and to make it difficult to form a desired cross section accurately. In view of this, the upper limit of the thickness (t) of the rubber strip (S) is preferably not more than 5 mm, more preferably not more than 4 mm. Similarly, the upper limit of the width (W) of the rubber strip (S) is preferably not more than 50 mm, more preferably not more than 40 mm.
When the surface 13 is an inclined surface 13 where a thickness varies, the front end edge 10 of the inclined surface 13 may be disposed, in plan view, perpendicularly to the longitudinal direction line as shown in
As shown in
As shown in
if the angle α of the inclined end edge 10e is less than 10 degrees, the rigidity of the tip (T) of the rubber strip (S) is degraded to make the end portion (e1) or (e2) unstable in shape and difficult to handle. If, on the other hand, the angle α of the inclined end edge 10e exceeds 80 degrees, the effect of circumferentially distributing the variation in mass is degraded, which leads to degradation of the effect of discharging air. In view of this, the lower limit of the angle α is more preferably not less than 25 degrees, further more preferably not less than 30 degrees. The upper limit is preferably not more than 75 degrees, more preferably not more than 60 degrees.
As shown in
a) and 10(b) show other embodiments of winding the rubber strip (S) while the embodiment shown in
In the embodiment shown in
Next, the rubber strip (S) can be produced by various methods. For example,
The production apparatus 20 includes:
a rubber extruder 21 for kneading rubber materials and continuously extruding the rubber materials in the form of a ribbon;
a calendar roll 22 disposed at a downstream side of the rubber extruder 21 and having a pair of rolls 22a and 22b capable of pressing and molding the rubber extruded from the rubber extruder 21 to have a finished cross sectional shape of the rubber strip (S);
a driving conveyer 23 for conveying the rubber strip (S) molded at the calendar roll 22; and
a cutting apparatus 24 disposed at a downstream side of the driving conveyer 23 and capable of cutting the rubber strip (S).
At a downstream side of the cutting apparatus 24, an applicator 25 for guiding the rubber strip (S) and a molding drum 26 onto which the rubber strip (S) is wound are disposed. The applicator 25 is axially movable relative to the molding drum 26 by a moving mechanism, not shown. This enables the rubber strip (S) to be guided to a predetermined winding position on the molding drum 26. Preferably, an accumulator 27 is disposed where needed between the driving conveyer 23 and the cutting apparatus 24.
The cutting apparatus 24 has a cutting device 24a disposed above the rubber strip (S) and movable upward and downward, and a conveyer 24b disposed under the rubber strip (S) and for receiving the cutting device 24a when lifted downward.
As shown in
In this example, the cutting edge 30 has a width (CW) that is larger than the length for cutting the rubber strip (S) while having a height (h) that is smaller than a thickness (t) of the rubber strip (S), as shown in
Pressing the cutting device 24a downward starts cutting of the rubber strip (S) with the cutting edge 30 first cutting into the surface of the rubber strip (S). Pressing the cutting device 24a farther downward completely cuts the rubber strip (S). Here the height (h) of the cutting edge 30 is smaller than the thickness (t) of the rubber strip (S). Thus, in the completely cut state, the pressing face 21a presses the end portions (e1) and (e2) of the rubber strip (S) each into a tapering shape, and the above-mentioned end surface 12 is formed as the inclined surface 13. That is, the cutting device 24 a is capable of cutting the rubber strip (S) while at the same time processing the end portions (e1) and (e2) each into a tapering shape, thereby improving productivity.
Cutting of the rubber strip (S) may be carried out while the conveyer 24b is suspended. Here the rubber strip (S) continuously supplied via the driving conveyer 23 is accumulated at the accumulator 27. Alternatively, the rubber strip (S) may be cut without suspending the conveyer 24b in order to improve productivity.
It is possible that the rubber strip (S) be easily cut by a slight cut on the surface of the rubber strip (S) by the cutting edge 30 when, for example, there is a relatively large degree of tension on the rubber strip (S). This precludes sufficient pressing of the rubber strip (S) by the pressing face 21a for accurate formation of the inclined surface 13. In this case, the cutting edge 30 is preferably provided with, somewhere on part thereof, at least one notch 33 that gives an intermission to the continuity of the cutting edge 30, as shown in
As shown in
While description has been made of the embodiments of the present invention, the illustrated embodiments should not be construed as to limit the scope of the present invention; various modifications are possible without departing from the scope of the present invention.
Tread rubbers were formed by spirally winding rubber strips specified in Table 1. The tread rubbers were used to produce 10000 pneumatic tires for passenger cars for each of the specifications in Table 1. The size of the tires was 215/45ZR17. The tires were tested for uniformity, disfiguration caused by air pocketing, and productivity. The test methods are as follows.
<Disfiguration>
The surface of the tread rubber after vulcanization was visually inspected for damage on the surface mainly caused by the second end portion of the rubber strip and for swelling mainly caused by internal air pocketing The recorded results are represented by the number of occurrences of damage and swelling. A smaller value indicates a more preferably result.
<Uniformity>
Radial Force variation (RFV) was measured for each test tire according to uniformity test conditions specified in JASO C607: 2000. For RFV, an overall at a low speed rotation (10 km/h) was used. A smaller RFV value indicates superior uniformity.
<Productivity>
The time required for forming the rubber member for the tread rubber was measured. A result is represented by an index on the basis that Comparative Example (A1) is 100. A larger value indicates a shorter period of time. The test results are shown in Table 1.
The test results confirmed that the tires according to Examples had superior uniformity and appearance performance to those of Comparative Examples.
Clinch rubbers were formed by winding rubber strips specified in Table 2 in the manners shown in
<Disfiguration>
The surface of the clinch rubber after vulcanization was visually inspected for damage on the surface mainly caused by the second end portion of the rubber strip and for swelling mainly caused by internal air pocketing. The recorded results are represented by the number of occurrences of damage and swelling. A smaller value indicates a more preferably result.
<Uniformity>
Radial Force Variation RFV was measured for each test tire according to uniformity test conditions specified in JASO C607: 2000. For RFV, an overall at a low speed rotation (6.8 km/h) was used. A smaller RFV value indicates superior uniformity.
The test results confirmed that the tires according to Examples had superior uniformity and appearance performance to those of Comparative Examples.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-154252 | Jun 2007 | JP | national |
| 2007-220022 | Aug 2007 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2008/060607 | 6/10/2008 | WO | 00 | 11/20/2009 |
